Can’t I multitask at least a little?

One of the questions that arises almost every time a new Kanban system comes to live is something like “But if I work on tasks in different stations (columns) then my personal WIP-limit has to be bigger than one, right?”

Well…

Let me answer this by a simple calculation:

Given the cold hard truth that multitasking actually means task-switching there is a very simple formula to calculate your effectiveness for the average task you are working on:

If n is the number of concurrent tasks, then each task is idling around (n-1)/n of the time.

If you work on one task at a time this formula yields zero. Because the task is never left neglected and you work on it all the time.

If you work on two tasks at a time, each of them is idling around 1/2 the time. On average.

If you work on three tasks at a time, each of them is idling around 2/3 of the time. On average.

If you work on eight tasks at a time, each of them is idling around 7/8 of the time. On average.

Or to put it in percentages

  • 1 task: 100% active, 0% idle
  • 2 tasks: 50% active, 50% idle
  • 3 tasks: 33% active, 66% idle
  • 8 tasks: 12,5% active, 87,5% idle

This means that a task that would take an hour on average will take 8 hours if you multitask 8 fold. On average. And that’s not even taking any costs into account for context switching!

So, yes can multitask a little, but –like magic– multitasking comes at a price. Be sure you are willing to pay it.

till next time
  Michael Mahlberg

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